A bogie for a double-axle bottom-mounted axle-type straddle-type monorail train

Abstract

This invention relates to a bogie for rail transit vehicles, specifically a bottom-mounted wheel-axle straddle-type monorail train bogie with two parallel axles. The purpose of this invention is to solve the problem of connecting the axle to the original gearbox output shaft within the limited axial space of a monorail train. By using a double-splined drive shaft and designing a connection and fixing method between the double-splined drive shaft, the hollow axle, and the gearbox, the axial space utilization is reduced, thus solving the connection problem between the axle and the gearbox output shaft. It also solves the problem of shortened bearing life and increased operating resistance caused by axial deviation between the axle and the gearbox output shaft. Furthermore, the elastic deformation of the long shaft compensates for the difficulty in ensuring installation accuracy due to large differences in axial dimensions. In addition, this invention also solves the problem of rapid wheel replacement in monorail trains, saving time on wheel replacement maintenance and improving work efficiency.

Description

Technical Field

[0001] This invention relates to a bogie for rail transit vehicles, specifically a straddle-type monorail bogie with parallel double-arm support and lower wheel axle type. It aims to solve the problems of quick wheel changing and bearing replacement in existing straddle-type monorail train bogies, and at the same time solve the problem of connecting the newly invented simply supported axle with the original gearbox output shaft. Background Technology

[0002] A monorail is a railway system with only one track. A straddle-type monorail is a transportation system where vehicles straddle a single beam. The advantages of monorail rail transit include low noise, small turning radius, strong climbing ability, low construction cost, and extremely flexible routes. It is well-suited to the natural conditions of mountainous cities and provides convenience for people's lives. As a type of urban rail transit, straddle-type monorails have a large passenger capacity and high safety requirements. Therefore, the quality and performance of the running wheels are crucial for their operation. However, because monorails are mostly built in mountainous areas with complex operating conditions, the actual service life of the running wheels is far shorter than the design life, increasing the frequency of tire replacement. Currently, the wheel replacement efficiency of monorail vehicles is low, and the process of replacing running wheels is time-consuming, affecting the normal operation of monorail trains. Therefore, developing a rapid wheel replacement mechanism is necessary.

[0003] With social progress and the rapid development of rail vehicle technology, it is moving towards a higher level of automation; this also puts forward higher requirements for the maintenance and upkeep of rail vehicles; the maintenance and upkeep of monorail vehicles must develop towards greater reliability and improved efficiency.

[0004] However, designing a separate quick-change mechanism would be costly and time-consuming, making it difficult to implement. A more ideal solution is to modify the existing straddle-type monorail train bogies to reduce both the cost and difficulty of the modification.

[0005] Modifying the existing straddle-type monorail train bogie axle support method (i.e., changing from an upper cantilever axle method to an undermount simply supported axle method—with bearings mounted at both ends of the axle) faces the challenge of connecting the axle with the original gearbox output shaft. Therefore, the innovation of this technical solution lies in solving the problem of connecting the axle with the original gearbox output shaft within a narrow axial space, thereby achieving the transformation of the undermount bogie for quick wheel changes while largely maintaining the original bogie structure. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to realize the connection between the axle and the original gearbox output shaft within a limited axial space dimension, thereby realizing the design of a straddle-type monorail train bogie with double-arm support and lower-mounted wheel axle, which can improve the efficiency of rapid wheel changing.

[0007] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution:

[0008] A double-axle, bottom-mounted wheel-axle straddle-type monorail train bogie includes: a double-arm bottom-mounted axle frame assembly, back-to-back mounted running wheels and their end axle box axle assembly assemblies, and a double-arm bottom-mounted axle frame lower bearing assembly. The running wheels and their end axle box axle assembly comprises a double-wheel back-to-back connecting hub intermediate flange assembly, a running wheel assembly, a double-row tapered roller bearing and sealing sleeve assembly, a double-wheel back-to-back running wheel hollow axle, and a double-end splined shaft assembly. The double-end splined shaft assembly is fitted onto the double-wheel back-to-back running wheel hollow axle. The hollow axle of the double-wheel back-to-back traveling wheel is mounted on the gooseneck frame support arm via tapered roller bearings. The two traveling wheels of the traveling wheel assembly are connected by a double-wheel back-to-back connecting hub intermediate flange assembly. The double-row tapered roller bearing and the sealing mounting sleeve assembly sit on the lower bearing of the lower axle frame. The lower bearing of the lower axle frame is bolted to the gooseneck frame support arm to achieve the purpose of disassembling and assembling the wheel axle from the bottom. The two ends of the double-splined drive shaft of the double-end splined shaft assembly are respectively splined to the hollow axle and the splined hub shaft, so that the axle is connected to the gearbox output shaft.

[0009] Furthermore, the double-splined shaft assembly consists of a drive shaft expansion plug, bolts, a double-splined drive shaft intermediate support rubber ring, and a double-splined drive shaft. The left end of the double-splined drive shaft is anchored to the inner splined hole arm of the hollow axle by the drive shaft expansion plug and bolts. The double-splined drive shaft intermediate support rubber ring is installed between the double-splined drive shaft and the hollow axle of the traveling wheel to prevent lubricating oil in the gearbox from leaking through the hollow axle of the traveling wheel and the double-splined drive shaft to the left side of the double-splined shaft.

[0010] Furthermore, the double-spline drive shaft is cut with one to four long slots along the axial direction, which facilitates the close fit between the hollow axle of the traveling wheel and the double-spline drive shaft, and transmits torque to the hollow axle. Its function is to transmit torque and provide axial positioning.

[0011] Furthermore, the right end of the double-ended spline drive shaft is connected to the inner spline of the output gear in the gearbox using an involute spline. Its function is to transmit torque, axially release, and has no axial positioning function.

[0012] Furthermore, the double-wheel back-to-back connecting intermediate flange assembly consists of an intermediate wheel hub flange with a tapered hole interference fit connection and a locking nut. The intermediate wheel connecting flange is designed with a tapered hole and installed on the hollow axle of the traveling wheel. It is then locked with the locking nut to ensure that the intermediate flange is fastened to the hollow axle of the traveling wheel, thus completing the radial and axial positioning. Tire bolts are embedded in the connecting flange for use as the hub of the traveling wheel.

[0013] Furthermore, the double-arm under-mounted axle frame assembly comprises a double-arm under-mounted axle frame, a double-arm under-mounted axle frame lower clamping plate, and a gearbox interface plate. The axle support arm of the double-arm under-mounted axle frame is designed in a gooseneck shape. Below it, the lower clamping plate assembly of the under-mounted axle frame is bolted to the double-arm under-mounted axle frame to complete the fixed connection of the axle box, realize the under-mounted function of the running wheel axle, and thus achieve the purpose of quick wheel changing.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] 1. The double-arm supported, bottom-mounted wheel axle monorail bogie of this invention solves the problem of connecting the axle and gearbox output shaft by using a hollow axle with splines inside and a double-end splined shaft to connect the axle and gearbox output shaft. It effectively utilizes the elastic deformation compensation of the long shaft to address the problems of reduced bearing life and increased operating resistance torque caused by coaxiality errors between the axle and gearbox output shaft; it also compensates for the problem of insufficient installation accuracy due to excessive coaxiality errors.

[0016] 2. This invention solves the problem of connecting the axle and the gearbox output shaft caused by the use of a bottom-mounted wheel axle type monorail bogie. By adopting a bottom-mounted wheel axle design for straddle-type monorail train bogies, the bottom-mounted wheel axle solution eliminates the step of hoisting from above the bogie during the disassembly, maintenance, replacement, and installation of the running wheels, thus saving time and manpower. This allows monorail trains to save a significant amount of time during wheel replacement maintenance and improves wheel replacement efficiency.

[0017] 3. This invention, through the successful design of a double-arm supported, lower-mounted wheel axle type monorail bogie, has successfully improved the efficiency of running wheel replacement and maintenance, further enhancing the economic efficiency of straddle-type monorail trains and facilitating the promotion of monorail train use. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings:

[0019] Figure 1 This is a schematic diagram of the device described in this invention;

[0020] Figure 2This is a schematic diagram of the double-arm supported under-mounted wheel axle monorail bogie assembly described in this invention;

[0021] Figure 3 This is an isometric view of the double-arm lower shaft frame assembly described in this invention;

[0022] Figure 4 This is a part drawing of the double-arm under-mount shaft frame described in this invention;

[0023] Figure 5 This is an exploded view of the straddle-type monorail train running wheels and axle assembly described in this invention;

[0024] Figure 6 This is an exploded view of the running wheel axle of the straddle-type monorail train described in this invention;

[0025] Figure 7 This is the isometric view of the hollow axle described in this invention;

[0026] Figure 8 This is a cross-sectional view of the wheel and axle assembly and the running wheel described in this invention;

[0027] Figure 9 This is a cross-sectional schematic diagram of the connection between the wheel and axle assembly and the gearbox according to the present invention;

[0028] Figure 10 This is an isometric view of the large gear and its splined hub in the transmission system described in this invention;

[0029] Figure 11 This is an exploded view of the gearbox and frame assembly as described in this invention.

[0030] In the diagram: 1. Double-arm under-shaft frame assembly; 2. Running wheel and its two end axle boxes axle assembly; 3. Double-arm under-shaft frame lower bearing assembly; 4. Gearbox interface plate; 5. Double wheel back-to-back connecting hub intermediate flange assembly; 6. Running wheel assembly; 7. Double row tapered roller bearing and sealing sleeve assembly; 8. Running wheel hollow axle; 9. Double-end splined shaft assembly; 10. Drive shaft expansion plug; 11. Bolt; 12. Double-end splined drive shaft intermediate support rubber ring; 13. Double-end splined drive shaft; 14. Hollow axle spline; 15. Large gear splined hub shaft; 16. Gearbox interface plate.

[0031] a. Hollow axle, b. Double-ended splined shaft and sealing ring, c. Expanding involute spline connection fixing anchor end, expansion cone and clamping bolt, d. Tapered roller bearing, e. Gooseneck frame support arm, f. Tapered bore hub and lock nut, g. Rubber tire and rim, h. Transmission system (drive motor and flexible coupling, driving bevel gear, driven bevel gear and secondary reduction gear), i. Output gear splined hub shaft (connected to the right end of the double-ended splined shaft via spline), j. Gearbox housing, k. Gearbox fixing screws Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings:

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The embodiments listed below are merely for further understanding and implementation of the technical solution of the present invention and do not constitute a further limitation on the claims of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication of two components; and they can refer to flexible connections, rigid connections, or movable links. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] This invention designs a double-arm supported, bottom-mounted wheel axle type monorail bogie to solve the problem of connecting the axle with the original gearbox output shaft within a limited axial space. It also enables rapid wheel replacement for monorail trains, reduces wheel replacement time, and improves the efficiency of wheel replacement and maintenance.

[0036] Previously, straddle-type monorail train bogies were designed with an upper axle structure for simplicity in design and manufacturing, and to facilitate transmission. However, this structure resulted in a significant workload when replacing and maintaining the running wheels. Disassembling the upper-mounted axle required hoisting the running wheels from above the bogie to the maintenance position, a time-consuming process. This invention designs a double-axle-supported, lower-mounted straddle-type monorail train bogie. When disassembling the running wheels, they can be directly removed from below to the maintenance position, avoiding the hoisting step, simplifying the process, and saving time. The double-axle-supported, lower-mounted straddle-type monorail train bogie mainly includes a double-arm lower-mounted axle frame assembly 1, back-to-back mounted running wheels and their end axle box axle assembly 2, a double-arm lower-mounted axle frame lower bearing assembly 3, and all other components except for the replacement of the above three assemblies. A key issue to address when using a bottom-mounted axle structure is the connection between the axle and the gearbox output shaft. This invention solves this problem by employing a splined half-shaft (double-ended splined drive shaft 9), thereby reducing the axial length required for the connection between the axle and the gearbox output shaft. The double-ended splined shaft achieves axial positioning at its left end (using an anchoring connection method; this end uses an involute spline to transmit torque to the hollow axle, and a shrinking cone expands the left end of the half-shaft against the inner spline hole wall of the hollow axle, providing centering and axial positioning anchoring). The right end of the half-shaft is connected to the spline hole of the gearbox output gear using an involute spline, serving to transmit torque, but is axially open and does not provide axial positioning. Multiple sealing rings are used in the middle section of the half-shaft to prevent gearbox lubricating oil from leaking through the half-shaft to its left side. Furthermore, due to the coaxiality error between the axle and the gearbox output shaft, problems such as affecting the bearing life of both and increasing the operating resistance torque will occur. This invention solves the problem of excessive coaxiality deviation between the two shafts and difficulty in ensuring installation accuracy by compensating for the elastic deformation of the long shaft.

[0037] The double-arm under-axle frame assembly described in the technical solution consists of a double-arm under-axle frame 1 as the framework. Additionally, the lower bearings 3 of the double-arm under-axle frame and the gearbox interface plate 16 are mounted on the double-arm under-axle frame for mounting the gearbox and axle. Four guide wheels are installed at the four corners of the double-arm under-axle frame assembly, and two more guide wheels are installed in the middle section of the frame assembly, extending downwards through two support arms. Two air springs are also installed above the support arms. Four traveling wheels are installed in the middle of the frame assembly, with two traveling wheels on each axle.

[0038] The double-arm under-axle frame assembly 1 supports the axle of the running wheels. Below the axle are double-sided under-axle frame lower clamps 3. The purpose of setting the lower clamps is to facilitate disassembly, thereby enabling the axle to be removed, and thus achieving quick disassembly and replacement of the running wheels, improving maintenance efficiency. A disadvantage of the under-axle frame assembly is that the transmission system is prone to interference. This invention addresses this by designing a hollow axle 8 with splines inside, and connecting the axle to the gearbox output shaft via a double-end splined shaft 9. This achieves a better connection between the axle and the gearbox output shaft within a limited axial space. The different axial misalignment between the axle and the gearbox output shaft affects the life of their bearings and also brings installation difficulties due to increased operating resistance torque. The elastic deformation of the long shaft can be compensated for, thus solving the problem of excessive coaxiality error and the difficulty in ensuring installation accuracy.

[0039] The double-arm lower axle frame assembly 1 and the double-side lower axle frame lower clamping brackets 3 together fix the axle position, and together with bearings, end caps and other parts, they achieve the fixation of the running wheel position;

[0040] See Figure 1 The diagram below illustrates the principle of the device described in this invention. Since the gearbox and frame are rigidly connected by bolts, no coupling is used between the axle and the gearbox output shaft to shorten the axial space. Therefore, the coaxiality error between the axle and the gearbox output shaft will cause increased torque during operation and will also affect the service life of the axle and bearings. Therefore, the axle is designed as a hollow axle with a double-splined shaft. The double-splined shaft is connected to the gearbox output shaft (splined hub shaft) via the spline on the right end of the double-splined shaft. A tapered expansion plug is used at the left end of the double-splined shaft to expand it, ensuring a tight fit between the outer spline on the left side of the double-splined shaft and the inner spline on the hollow axle, thereby transmitting torque. The effect of coaxiality error can be mitigated by the elastic deformation of the double-splined shaft. Multiple sealing rings are installed between the double-splined shaft and the hollow axle to prevent the gearbox's lubricating oil from leaking through the double-splined shaft to its left side.

[0041] See Figure 2 The double-arm supported lower-mounted wheel axle type monorail bogie of this invention is mainly composed of a double-arm lower-mounted axle frame assembly and a bogie braking and transmission assembly; combined with Figure 2 The double-arm lower axle frame assembly mainly consists of the double-arm lower axle frame assembly 1, the back-to-back mounted running wheels and their two end axle boxes axle assembly 2, the double-arm lower axle frame lower bearing assembly 3, and all the components of the bogie of a certain city's monorail line 2 and 3 train except for the above three assembly assemblies which are replaced. It mainly supports the running wheels, carries the bogie braking system and transmission system, and also plays a guiding role through the guide wheels.

[0042] See Figure 4 The figure shows a part of the double-arm under-mounted axle frame described in this invention. The double-arm under-mounted axle frame in this invention provides assembly space for the running wheel axle by designing a gooseneck frame support arm, and can achieve the purpose of under-mounting the running wheel and its axle by installing and connecting it with the lower clamping bracket 3 of the double-sided under-mounted axle frame.

[0043] See Figure 5 This is an exploded view of the straddle-type monorail train running wheel and axle assembly described in this invention. Each axle has two running wheels 6 connected back-to-back by a connecting hub intermediate flange assembly. The axle 8 is a hollow axle, containing splines to maintain radial position with the double-end splined shaft assembly 9. The axle is mounted on the lower bearing 3 of the double-sided lower axle frame via a double-row tapered roller bearing and a sealing mounting sleeve assembly 7. The hub intermediate flange of the back-to-back double-wheel connection uses a tapered design and is secured with a lock nut to ensure axial positioning of the running wheels on the axle.

[0044] See Figure 6 The double-splined shaft assembly consists of a drive shaft expansion plug 10, bolts 11, a double-splined drive shaft intermediate support rubber ring 12, and a double-splined shaft 13. The support rubber ring is used to fix the axial position of the double-splined shaft 13 and the hollow axle 8. The drive shaft expansion plug 10 is placed inside the double-splined shaft 13 to keep the position of the double-splined shaft and the hollow axle relatively fixed. The bolts 11 ensure that the position of the drive shaft expansion plug on the outward side is fixed.

[0045] See Figure 7 The diagram shows a cross-sectional view of the wheel and axle assembly and the running wheel described in this invention. The axial positioning of the double-splined shaft 9 is at the left end of the half shaft, which adopts an anchoring connection method. The torque is transmitted to the hollow axle 8 using an involute spline at this end. The transmission shaft expansion plug 10 expands the left end of the half shaft to the inner spline hole wall of the hollow axle 8, which plays a role in centering and axial positioning.

[0046] See Figure 8 The diagram shows a cross-sectional view of the wheel and axle assembly and the connection between the running wheel and the gearbox as described in this invention. The splined hub shaft on the large gear of the gearbox and the hollow axle are connected by a double-ended splined shaft to achieve the purpose of connection and to transmit torque; it is axially open and has no positioning function.

[0047] See Figure 9 This is a schematic diagram of the splined hub shaft described in this invention.

[0048] See Figure 10 This is a schematic diagram of the connection between the gearbox and the double-arm lower shaft frame. The gearbox and the frame are connected through a gearbox interface plate. The gearbox is connected to the interface plate by bolts, and the interface plate is then connected to the frame by bolts. All of these connections are rigid connections.

[0049] Working principle:

[0050] When the bogie is in operation, the traction motor provides power, which is connected to the splined hub shaft 15 by bolts through a large gear. The splined hub shaft also serves as the output shaft of the gearbox. The splined hub shaft is connected to the hollow axle 8 through a double-ended splined shaft 9. Through this path, power is transmitted from the motor to the running wheels 6. The use of the splined hub shaft, the splined shaft, and the hollow axle achieves the purpose of power transmission. More importantly, no coupling is used at the connection between the axle and the gearbox output shaft, saving axial space of the bogie.

[0051] The axial positioning of the double-splined shaft 9 is at the left end of the half-shaft, using an anchoring connection. This end uses an involute spline to transmit torque to the hollow axle 8. An expanding cone 10 expands the left end of the half-shaft against the inner spline hole wall of the hollow axle 8, providing centering and axial anchoring. One to four long slots are cut axially at the left end of the half-shaft to ensure a more reliable fit between the involute spline of the double-splined shaft and the inner wall of the involute spline hole of the hollow axle. The right end of the half-shaft is connected to the spline hole of the gearbox output gear using an involute spline, serving to transmit torque. It is axially open and does not provide axial positioning. Multiple sealing rings are used in the middle section of the half-shaft to prevent gearbox lubricating oil from leaking through the half-shaft to its left side.

[0052] When the bogie is under maintenance, it is towed to a dedicated maintenance station, where the lower bearing 3 of the lower axle frame is disassembled, allowing the axle and running wheels to be removed for maintenance. This saves time and improves work efficiency compared to existing solutions.

[0053] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A double-axle, bottom-mounted wheel-axle type straddle-type monorail train bogie, characterized in that, include: The assembly comprises a double-arm under-mounted axle frame assembly, back-to-back mounted running wheels and their end axle box axle assembly assemblies, and a double-arm under-mounted axle frame lower bearing assembly. The running wheels and their end axle box axle assembly consists of a double-wheel back-to-back connecting hub intermediate flange assembly, a running wheel assembly, a double-row tapered roller bearing and sealing sleeve assembly, a double-wheel back-to-back running wheel hollow axle, and a double-end splined shaft assembly. The double-end splined shaft assembly is fitted onto the double-wheel back-to-back running wheel hollow axle, and the double-wheel back-to-back running wheel hollow axle is connected via a double... The tapered roller bearing is mounted on the gooseneck frame support arm. The two running wheels of the running wheel assembly are connected by a double-wheel back-to-back hub flange assembly. The double-row tapered roller bearing and the sealing mounting sleeve assembly sit on the lower bearing of the lower axle frame. The lower bearing of the lower axle frame is bolted to the gooseneck frame support arm to achieve the purpose of disassembling and assembling the wheel axle. The two ends of the double-splined drive shaft of the double-end splined shaft assembly are respectively connected to the hollow axle and the gearbox output shaft, i.e., the splined hub spline, so that the axle is connected to the gearbox output shaft. The double-splined shaft assembly consists of a drive shaft expansion plug, bolts, a double-splined drive shaft intermediate support rubber ring, and a double-splined drive shaft. The left end of the double-splined drive shaft is anchored to the inner splined hole arm of the hollow axle by the drive shaft expansion plug and bolts. The intermediate support rubber ring of the double-splined drive shaft is installed between the double-splined drive shaft and the hollow axle of the traveling wheel to prevent the lubricating oil in the gearbox from leaking through the hollow axle of the traveling wheel and the left side of the double-splined drive shaft.

2. A double-axle, bottom-mounted wheel-axle type straddle-type monorail train bogie according to claim 1, characterized in that, The double-spline drive shaft is cut with one to four long slots along the axial direction, which facilitates the close fit between the hollow axle of the traveling wheel and the double-spline drive shaft, and transmits torque to the hollow axle. Its function is to transmit torque and provide axial positioning.

3. A double-axle, bottom-mounted wheel-axle type straddle-type monorail train bogie according to claim 1 or 2, characterized in that, The spline hub connection between the right end of the double-ended spline drive shaft and the gearbox output shaft is an involute spline connection, which is used to transmit torque, axially open, and without axial positioning.

4. A double-axle, bottom-mounted wheel-axle type straddle-type monorail train bogie according to claim 1, characterized in that, The double-wheel back-to-back connecting intermediate flange assembly consists of an intermediate wheel connecting flange with a tapered hole interference fit and a lock nut. The intermediate wheel connecting flange is designed with a tapered hole and installed on the hollow axle of the traveling wheel. It is then locked with the lock nut to ensure that the intermediate wheel connecting flange is firmly fixed on the hollow axle of the traveling wheel, thus completing radial and axial positioning. Tire bolts are embedded in the intermediate wheel connecting flange for use as the hub of the traveling wheel.

5. A double-axle, bottom-mounted wheel-axle type straddle-type monorail train bogie according to claim 1, characterized in that, The double-arm lower axle frame assembly consists of a double-arm lower axle frame, a double-arm lower axle frame lower bearing, and a gearbox interface plate, wherein the axle support arm of the double-arm lower axle frame is designed in the form of a gooseneck. Below it, the lower bearing assembly of the double boom under-mounted axle frame is bolted to the double boom under-mounted axle frame to complete the fixed connection of the axle box, realize the under-mounted function of the running wheel axle, and thus achieve the purpose of quick wheel changing.

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